The invention relates to a traction mechanism drive, for example, a control drive of an internal combustion engine, with an endless traction mechanism, for example, a link chain, connecting a driving gear and at least one driven gear with a positive fit, wherein at least one tensioning device actuated by a pressure medium and one guide rail are arranged on the periphery of this traction mechanism, wherein at least the guide rail has a carrier body and a resiliently flexible sliding body connected to the carrier body on the side of the traction mechanism, and wherein a spring element is arranged in a free space between the upper side of the carrier body and a lower side of the sliding body.
Such traction mechanism drives are used, for example, for timing and/or auxiliary assembly drives in internal combustion engines. The traction mechanism, for example, a link chain, is here driven by a driving gear mounted on a crankshaft of the engine and the traction mechanism itself drives driven gears that are connected to timing shafts or camshafts of the engine. For reducing transverse vibrations of the traction mechanism, it is guided by a guide on its tensioned side that extends to the driving gear, the so-called loaded belt section, and loaded by a tensioning device with a force tensioning the link chain on the slack side that runs out from the driving gear, the so-called slack belt section.
Traction mechanism drives typically span relatively large distances between the crankshaft and the one or more camshafts. In order to prevent vibrations of the link chain in the driving plane, the link chain is guided on at least one guide rail in the regions between the mentioned shafts. For this purpose, a chain tensioner transmits its force via a moving tensioning rail to the link chain. In contrast, the guide rail arranged in the region of the loaded belt section is connected fixed in position with the engine. Here, the link chain slides over the guide rail that is usually made from an elongated carrier body arranged laterally parallel to the loaded belt section and mounted fixed on the housing, wherein this carrier body is made from a light-metal alloy or a fiber-reinforced plastic material, and from a sliding body mounted on the carrier body on the side of the traction mechanism, wherein this sliding body is made from a low-friction and wear-resistant plastic. The guide rail is used essentially for suppressing radial impact and oscillation movements of the traction mechanism and thus for avoiding large dynamic loads and a great generation of noise by the traction mechanism drive.
Nevertheless, previously it had not always been avoided that especially in the case of material-fatigued traction mechanisms in the form of link chains, relatively high dynamic forces in the form of vibrations and oscillating impact movements act on the guide rail that cannot be damped under all conditions, so that, despite the presence of springs and other damping elements in the guide rail or in the chain tensioner, vibrations are generated that negatively affect the service life of the traction mechanism drive.
From DE 198 56 705 A1, a guide device for a link chain of a chain drive is known in which guide elements are continued as an elastic mass element past their guiding length, without the chain continuously contacting the guide elements in their continued region. In the case of an embodiment according to FIG. 2 in that document, two ends of the guide element are formed as inherently elastic projections that are used for damping chain vibrations. Spring elements for damping are not provided in this reference.
From EP 0 055 166 B1, a mechanical tensioning device for drive chains is known that comprises a ramp that is formed by at least one curved spring leaf having a sliding surface and that is set elastically against the chain and that is also provided with anti-reverse-motion means for preventing recoil of the ramp. The spring leaf, consisting of spring steel, is fixed at its ends on a metallic carrier that is fixed rigidly on a housing part of an internal combustion engine.
From US 2005/0239590 A1, a guide rail of a traction mechanism drive is known in which the guide rail is made from a convex shaped steel bar that is fixed rigidly with its ends on a housing part of an internal combustion engine. A sliding body made from flexible material is injection molded around the steel bar. By influencing the stiffness of the sliding body, vibrations of the link chain are to be damped.
From DE 43 27 314 A1, a chain tensioner is known with a leaf spring and a flange for exerting a tension on a chain, wherein the flange is made from a plastic that undergoes a creep deformation when it is exposed to a force at elevated temperatures, and wherein the flange has a pocket receiving the leaf spring between a first end and a second end that is closed at the first flange end and the second flange end and also along a first side of the flange and that is open along a second side of the flange for holding the leaf spring. In this way, the leaf spring is fixed mechanically so that it exerts a force on the flange, without any attachment means or recesses that could lead to concentrated-stress points having to be provided in the leaf spring. Furthermore, because the leaf spring is encapsulated in the pocket by three sides of the flange, the leaf spring is protected from contact with any clips or carriers to which the chain tensioner could be attached. This construction should contribute to increased strength of the flange, because the complete cross section of the flange receives the force of the spring at both ends. The result is a stronger flange that is less easily damaged during operation.
From U.S. Pat. No. 7,063,635 B2, a guide rail of a traction mechanism drive is known in which a leaf spring made from spring steel in pockets of an integral guide rail is placed parallel to the contact surface of the guide rail. The leaf spring should absorb at least a portion of the forces of the link chain acting on the guide rail.
Finally, from DE 10 2005 036 206 A1, a traction mechanism drive according to the class is known in which it is provided that the guide rail is constructed to be actuated at least partially normal to the traction mechanism, is loaded by at least one spring element in the direction toward the traction mechanism with an adjusting force, and is provided at least with one outer stop for limiting a control movement away from the traction mechanism. According to FIG. 4 in that document, a spring element is arranged between the sliding coating body and the carrier body. Here, movement of the sliding coating body is realized relative to the carrier body and normal to the traction mechanism, wherein this movement is limited in the direction toward the traction mechanism essentially by a release of tension in the spring element and in the opposite direction by the inside of the carrier body or the clamping of the spring element. Here, the body has a resiliently flexible construction, is connected rigidly to the carrier body in the region of one longitudinal-side end, and is held in the region of the opposite longitudinal-side end so that it can move tangentially on the carrier body. In this way, the sliding coating body is, on one hand, fixed reliably on the carrier body and, on the other hand, can adapt optimally to the appropriate adjustment path relative to the carrier body.
Also, the guide rail described in DE 10 2005 036 206 A1 has proven to have a complicated overall setup, because carrier bodies, sliding bodies, and the spring element are separate parts and are made from different materials. The damping potential also offers room for improvement.